In the field of integrated circuit manufacturing, it is well known in the art that in order to create semiconductor devices of various functionalities on a semiconductor substrate, the substrate will generally go through, at different stages, various chemical and mechanical processing. Such processing may include, for example, ion implantation and/or doping, chemical vapor deposition, isotropic and/or anisotropic etching, chemical-mechanical-polishing, etc. The processing may produce devices such as, for example, field-effect-transistor (FET), electronic fuse, random access memory (RAM), etc. In order to ensure integrity of the functionalities of various final products fabricated in a semiconductor wafer, which in general contains a plurality of semiconductor devices, non-destructive and/or in-situ testing at different processing stages is essential and generally preferred. A non-destructive in-site testing may timely provide vital information on processing conditions that may need to be adjusted during the course of manufacturing in order to control the quality of the final products, and to monitor possible development of device defects.
Non-destructive and/or in-site testing may be conducted directly on semiconductor devices in a wafer under development. Alternatively, it may be performed in one or more designated testing areas or testing strips on the same wafer whereupon the semiconductor devices are commonly produced. A testing strip may include one or more test structures embedded in between the semiconductor devices in order to closely resemble processing conditions experienced by the semiconductor devices. It is also conceivable that a test strip may be formed in a wafer different from that of the semiconductor devices but the test strip is placed closely to the wafer of the semiconductor devices during manufacturing and testing. On the other hand, among various non-destructive testing there is a surface voltage testing mechanism, which measures device parameters that may be used as a general indication as to the quality of electrical nodes and/or contacts often found in various semiconductor devices.
Currently, surface voltage testing is generally conducted by a Kelvin probe. Kelvin probe is a non-contact, non-destructive measurement device used to investigate properties of materials. A Kelvin probe, based on a vibrating capacitor, generally measures a difference in work functions (or for non-metals surface potentials) between a conducting specimen and a vibrating tip. The work function is extremely sensitive to the surface conditions and thus its reading may be adversely affected by, for example, absorbed or evaporated layers, surface reconstruction, surface charging, oxide layer imperfections, surface and bulk contamination, etc., to list a few. Because the work function is so sensitive, it is sometimes difficult to make proper differentiation and/or judgment between a voltage difference caused by actual conditions of the semiconductor device under test and that caused by changes in one or more of the many affecting factors.
Therefore, there exists a need in the relevant art to develop an effective non-destructive method for measuring surface voltage for device inspection during semiconductor device manufacturing.